Production of styrene and related compounds



April 22, 1958 F. D. MAYFIELD ETAL 2,831,907v

PRODUCTION OF STYRENE AND RELATED COMPOUNDS I Filed Dec. 10, 1956 KE C 5 REACTION m qfb PRODUCT} STEAM A 2.| LBS.

STEAM- 0.s7 LBS.

ETHYLBENZENE |.o LBS.

INVENTORS' FRANKLIN D. MAYFIELD JAIX ES CLIFFORD SHAW ATTORNEYS benzene is dehydrogenated to form styrene.

advantage of this procedure is that the extremely hot.

United States Patent PRODUCTION OF STYRENE AND RELATED COMPOUNDS Franklin D. Mayfield, Baton Rouge, La., and James Clifford Shaw, Dallas, Tex.

Application December 10, 1956, Serial No. 627,170 11 Claims. (Cl. 260669) This invention relates to an improved method of making styrene and related compounds by dehydrogenation of alkylatedaromatic hydrocarbons.

It is well known that styrene can be produced by rapidly passing a mixture of ethylbenzene and steam over a bed of a suitable catalyst at elevated temperature. Heretofore, however, it has been practice (1) to superheat the steam to a temperature above the reaction temperature, i. e., the temperature at which the ethylbenzene is dehydrogenated; -(2) to simultaneously and separately heat the ethylbenzene to a temperature below the reaction temperature; (3) thereafter to admix the steam and ethylbenzene in the correct proportions to yield the correct reaction temperature; (4) and then to pass the mixture to a catalyst-containing reactor wherein the ethyl- One dissteam, upon being admixed with the ethylbenzene, causes portions of the latter to be brought up almost to the temperature of the steam before mixing, and since the steam is at or above the temperature at which the ethylbenzene begins to pyrolyze, some of the ethylbenzene is destroyed by thermal cracking to produce undesired materials such as benzene, toluene, carbon monoxide, carbon dioxide, tar, carbon, and the like, instead of styrene, thus lowering the yield of styrene. A second important disadvantage is that high cost alloy equipment is required due to the fact that the steam is superheated to a relatively high temperature, e. g., usually in the range of 670 to 850 C. If the steam were kept at a lower temperature, it would be possible to utilize lower cost alloy equipment.

Accordingly, it is an object of the present invention to provide a method whereby ethylbenzene or other alkylated aromatic hydrocarbons may be dehydrogenated to produce styrene or homologues or analogues thereof, without appreciable side reaction production of carbon, tar, benzene, etc.

Another object of this invention is to provide a method of dehydrogenating ethylbenzene or other alkylated aromatic hydrocarbons in admixture with steam, wherein the temperature of the steam prior to admixture with the ethylbenzene or its related compounds is maintained at a temperature below the reaction temperature, thereby permitting the method to be carried out in lower cost alloy equipment.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description together with the accompanying drawing which is a How sheet schematically illustrating how styrene is produced.

The essential steps of the present invention, as applied, for example, to the production of styrene from ethylbenzene, are:

(1) Mixing ethylbenzene vapor with steam in accordance with a predetermined ratio at any suitable temperature,

2,831,907 Patented Apr. 22, 1958 the ethylbenzene with steam. This steam-ethylbenzene mixture is superheated to a temperature which is often around 610 C., after which the mixture is then passed through a catalyst containing reactor where the contact then is as indicated in the test data given below:

Range Test Test Run A Run B Ethylbenzene Flow (Lbs/hr. per cu.

ft. of Reactor Volume) 7-50 35. 4 26.6 Steam Flow (Lbs/hr. per cu. ft. of

Reactor Volume) 15 105 89. 5 B9. 1 Lbs. Steam/lb. Ethylbenzenm 1.5-20 2. 5 2. 6 Reactor Inlet Temperature, 540-650 607 610 Reactor Inlet Pressure, p. s. i. g 1-15 6 7 Weight Percent Styrene in Product 2060 41. 3 39. 5 Weight Percent Styrene in Feed 012 5. 7 4.0 Yield, mols Stryene/mol Ethylbenzene destroyed -95 92.0 94. 1

The process is normally continuous with the ethylbenzene and steam being constantly passed through the system.

The mixture passing out of the reactor is rapidly cooled to condense the styrene product and any unreacted ethylbenzene. The cooling may be brought about in a number of ways. Preferably this is accomplished by passing it through a heat exchanger adapted to transfer the heat removed from the reacted mixture to incoming ethylbenzene vapors and steam according to conventional heat exchange practice. Residual gases and water are first separated from the condensate and then the styrene is removed according to conventional practice. Preferably this is accomplished by fractionally distilling the mixture. The styrene and unreacted ethylbenzene are recovered as individual compounds and the unreacted ethylbenzene may be reintroduced into thesystem to produce additional styrene.

The following example is illustrative only of the present invention and, therefore, is not to be construed as limiting the invention.

Referring to the accompanying flow sheet, a mixture comprising 1.0 lb. of ethylbenzene and 0.67 pound of steam was passed in a steady flow through an ethylbenzene vaporizer A and a first heat exchanger B in succession. Also passing through the same first heat exchanger so as to impart heat to the vaporized ethylbenzene-steam mixture was the reacted mixture from the catalyst containing reactor C. The ethylbenzene-steam mixture passed out of the heat exchanger B at a temperature of about 420 C. Simultaneously 2.1 lbs. of steam were passed in steady flow through a second heat exchanger D and heated therein by the reacted mixture passing out from the first heat exchanger. The steam passed out of the second heat exchanger D at a temperature of about 335 C. This steam was then mixed with the ethylbenzene-steam mixture from the first heat exchanger, and the combined mixture was passed through a furnace E which caused it to be heated to a temperature of about 614 C. The combined mixture at a temperature of 614 C. was then passed rapidly through the reactor shell C which contained a ferrous oxide-potassium oxide catalyst. The total actual residence "time for the combined mixture in the reactor was about 0.1 second.

aesneor 3 The reacted mixture had a temperature of about 546 C. as it left the reactor. The reacted mixture was cool-ed by passing it through the first and second heat exchangers in turn, thereby heating the incoming ethylbenzene and steam, as previously described. The temperature of the reacted mixture as it passed out of the first heat ex- It has been determined that the present method can be operated with as little as 1.5 pounds of steam and as high as 20 pounds of steam or even more per pound of ethylbenzene. However, for practical reasons such as economy of operation, the preferred range is from two to three pounds of steam per pound of ethylbenzene.

As is to be expected, by similar procedure it is pos sible to dehydrogenate other alkylated aromatic hydrocarbons containing at least two carbon atoms in a side chain. Thus, for example, diethyl-benzen'e, isopropylbenzene, ethyl toluene, ethyl naphthalene, and ethylchlorobenzene, may be dehydrogenated to produce homologues or analogues of styrene. The procedure of the present invention may be executed at atmospheric pressures or at higher pressures, e. g. 40 pounds per square inch. In place of the ferrous oxide-potassium oxide, other well known catalysts may be utilized, e. g. catalysts of the type described in the patent to Hermann Mark et al., No. 2,110,833, issued March 8, 1938.

As stated hereinabove the necessary heat of reaction is applied to the ethylbenzene steam mixture by passing the mixture through a furnace. The temperature re quired for converting the ethylbenzene to styrene is lower when a catalyst is used than when no catalyst is used. At the temperature utilized in the present method, the ethylbenzene-steam mixture is subjected to little or no thermal cracking or pyrolysis prior to being intro duced into the reactor. Conversion of the ethylbenzene to styrene takes place when the mixture is passed over the catalyst. At the same time, since the ethylbenzene is already admixed with the steam, when it is heated to the required reaction temperature, it is subject to little or no local heating as is the case when the ethylbenzene is mixed with steam above the required reaction temperature. For this reason there is a higher yield of the desired product, styrene, and the quantity of undesired materials, such as tar, produced by thermal cracking is reduced to a quantity that prevents rapid fouling of the system.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. Therefore, it is to be understood that the invention is not limited in its application to the details specifically described or illustrated, and that within the scope of the appended claims it may be practiced otherwise than as specifically described or illustrated.

We claim:

1. The method of dehydrogenating an alkylated aromatic hydrocarbon containing at least two carbon atoms in a side chain which comprises mixing said hydrocarbon with steam, said hydrocarbon and steam each being at a temperature lower than dehydrogenation temperature prior to mixing, heating the mixture to a temperature within the range required for dehydrogenation, and contacting said heated mixture while at dehydrogenation temperature with a dehydrogenation catalyst.

2. The method of claim 1 wherein the alkylated aromatic hydrocarbon and steam are mixed at a temperature below 500 C. and said mixture is subsequently heated to a dehydrogenation temperature in the range of from 500 to 700 C.

3. The method of claim 1, wherein said hydrocarbon is ethylbenzene.

4. The method of claim 1 wherein the alkylated aromatic hydrocarbon is isopropyl-benzene.

5. The method of claim 1 wherein the alkylated aromatic hydrocarbon is Y diethyl-benzene.

6. The method of claim 1 wherein the alkylated aromatic hydrocarbon is ethyl toluene.

7. The method of claim 1 wherein the alkylated aromatic hydrocarbon is ethyl naphthalene.

8. The method which comprises dehydrogenating an alkylated aromatic hydrocarbon containing at least two A carbon atoms in a side chain, by mixing the same with steam having a temperature below dehydrogenation temperature, heating the mixture to a temperature within the range required for dehydrogenation, and contacting said heated mixture with a dehydrogenation catalyst.

9. The method of producing styrene by dehydrogenation of ethylbenzene which comprises the steps of mixing ethylbenzene having a temperature below dehydrogenation temperature with steam which has been superheated insufiiciently to supply the heat required for dehydrogenation, heating the ethylbenzene steam mixture to a temperature at which rapid dehydrogenation will occur, and contacting said heated mixture while at a dehydrogenation temperature with a dehydrogenation catalyst.

10. The method of claim 9, wherein said mixture is heated to a temperature of approximately'610" C.

11. The method of producing substantially water white and tar free styrene by dehydrogenation of ethylbenzene which comprises mixing ethylbenzene and steam at a temperature below 500 C., heating the resulting mixture to a temperature within the dehydrogenation range of from 500 to 700 C. and contacting said heated mixture while in said temperature range for a fraction of a second with a dehydrogenation catalyst.

References Cited in the file of this patent UNITED STATES PATENTS 2,683,180 Amos et al July 6, 1954 2,813,089 Twaddle et al. Nov. 12, 1957 2,813,137 Twaddle et a1. NOV. 12, 1957 FOREIGN PATENTS 635,827 Great Britain Apr. 19, 1950 

1. THE METHOD OF DEHYDROGENATING AN ALKYLATED AROMATIC HYDROCARBON CONTAINING AT LEAST TWO CARBON ATOMS IN A SIDE CHAIN WHICH COMPRISES MIXING SAID HYDROCARBON WITH STEAM, SAID HYDROCARBON AND STEAM EACH BEING AT A TEMPERATURE LOWER THAN DEHYDROGENATION TEMPERATURE PRIOR TO MIXING HEATING THE MIXTURE TO A TEMPERATURE WITHIN THE RANGE REQUIRED FOR DEHYDROGENATION, AND CONTACTING SAID HEATED MIXTURE WHILE AT DEHYDROGENATION TEMPERATURE WITH A DEHYDROGENATION CATALYST. 